Considering how successful the original Iron Man movie turned out to be, it seems pretty clear that director Jon Favreau could simply coast Iron Man 2 into theaters and moviegoers would flock to see it. But, instead of sitting back and letting momentum carry the sequel, Favreau sought out top-notch talents like Sam Rockwell and Mickey Rourke, actors' actors known for their nuanced performances.

Favreau recently admitted that he almost chose Rockwell to play the lead role of Tony Stark, which ultimately went to Robert Downey Jr., and specifically sought him out for Iron Man 2 because he needed someone who could give a performance that would stand up to Rourke's. Now, Downey, Jr. has weighed in on bringing in Rourke for the role of Ivan Vanko, aka Whiplash, in the sequel.

Downey, Jr. told The Independent that there was some resistance to Rourke's involvement in Iron Man 2 from both the studio and Rourke's own reps.

"We fought for Mickey to be in our film but then he fought for us because his people were, understandably, like, 'Hey! He's a really big deal right now, and we want to make sure that he's gonna be properly serviced.' And Mickey made some really great choices, which is why we hired him as 'bad guy' Ivan Vanko because we figured he would."

Downey, Jr. said that Rourke's intense research and dedication to acting really helped to bring Whiplash to life.

"I'm not fully a Method guy but I like playing around with that energy sometimes. And Mickey wanted to do his part in Russian; he had a dialect coach who taught him and translated, so that was a very unique take. From the very start, he said, 'I don't want it to be Dolph Lundgren from Rocky IV. I want to bring humanity and dimensions into it.' And I think he did that."

Downey, Jr. said that, beyond all of the hype surrounding the return to fame that both he and Rourke have experienced in recent years, they're ultimately just actors playing parts.

" How bad-ass was Mickey with those whips? But, really, at the end of the day, it's just two schmucks in trailers and once in a while I'd be like, 'Hey, mind if I used your treadmill?' And Mickey goes, 'Yeah, you should try my weight vest. Helps you break the sweat quicker.' And I'd be, 'OK. See you on set, bad guy,' and he'd say, 'OK, punk.' "

Iron Man 2 was written by Justin Theroux and also stars Don Cheadle, Samuel L. Jackson and Scarlett Johansson.